1. Field of the Invention
The present invention pertains to a blur correction apparatus for correcting an image blur, a control apparatus to be used in a blur correction apparatus, an image taking apparatus such as a camera, for example, capable of taking still images and/or moving images and having an image blur correction function, a control method to be used in these apparatuses, and a computer program product to be used with these apparatuses.
2. Related Background Art
Currently, in video cameras and the like having a blur correction function there is included at least a vibration detection means for detecting vibrating components, and a blur correction means for correcting an image blur in accordance with results of detection performed by the detection means.
Examples of the vibration detection means include directly detecting the vibrating components of the instrument by means of an angular velocity sensor, an angular acceleration sensor, etc., or an electronic method of detecting movement of the image by comparing the image across continuous fields or frames.
Examples of the blur correction means include optical types for mechanically correcting the optical axis, and electronic types for performing the correction by electronically selecting the range that is to be actually recorded or outputted (i.e., the cut out range) from the image that has been obtained.
In an electronic blur correction means there are such methods as, for example, saving in a memory an image that has been taken and then cutting out and enlarging a part thereof, or another method of using an image taking element which has a greater number of pixels than those of the standard image taking element required in the broadcasting format, and then cutting out a size therefrom which is equivalent to the standard size of the broadcasting format.
In consideration of blur prevention performance, the optical type in which the correction is continuously being made is more advantageous than the electronic type in which corrections are made per field; however, the optical type requires separate mechanical parts to perform the corrections, while the electronic type performs the corrections by means of a CDD or memory, so it is more advantageous for purposes of compact construction. Therefore, with video cameras and the like, in the case when priority is given to the compact construction, the blur correction is generally performed by means of the electronic type.
Thus, explanation will be made here regarding the electronic type of correction, and in particular, the method of using the image taking element which has a greater number of pixels than those of the standard image taking element required in the broadcasting format and then cutting out therefrom a size equivalent to that of the standard size of the broadcasting format.
FIG. 11 is a diagram depicting an image taking area of this image taking element. Reference numeral 501 is the entire image taking area of the image taking element, and reference numerals 502, 503 and 504 indicate the broadcasting format standard size. In the case when the blur correction is not performed, the area designated by 503, which is the center, is cut out and outputted as an image.
In the case when the blur correction is to be performed the cut out area is moved over to 502 or 504, for example, in response to a signal from the vibration detection means in order to remove the image blur, and then the image is outputted. The cut out position can be anywhere as long as it is within the entire image taking area 501.
FIG. 12 is a constructional diagram of a blur correction unit of a video camera or other image taking apparatus having a blur correction device in which the detection means is an angular velocity sensor and the blur correction means is of the electronic method. Hereinafter, explanation will be made following FIG. 1 regarding an image taking apparatus having the blur correction device.
Reference numeral 101 is a lens unit and reference numeral 102 is a solid image taking element (CCD). The subject image is imaged on the CCD 102 by means of the lens unit 101 and then an photoelectric conversion takes place with the CCD 102. Used as the CCD 102 here is a CCD having a greater number of pixels than in the standard CCD required in the broadcasting format (such as, for example, NTSC format). Reference numeral 104 is a CCD driving circuit and drives the CCD 102. The CCD driving circuit 104 obeys control instructions from the microcomputer 130 described below, so that it can make a selection in a V direction as to from which line the output area is ultimately to be cut out. Reference numeral 501 in FIG. 11 is the entire image size, and 502, 503 and 504 are examples of standard image sizes in accordance with broadcasting formats. If, for example, the area from line ya+1 that is Δya line below from the topmost line is considered to be valid then the line Δya is read out at high speed, and thus it is performed to read out from ya+1 at the same timing as in the case where a standard size CCD is used with respect to the vertical synchronization signal. Then, by reading out the remaining line Δyb at high speed, it is possible to cut out a standard-sized line in the V direction.
Reference numeral 103 is analog signal processing portion, and this performs predetermine processing on the signal obtained at the CDD 102 and generates an analog image taking signal. Reference numeral 103 may be a CDS circuit (i.e., a co-related double sampling circuit), an AGE circuit, etc. Reference numeral 106 is a memory, and this memory 106 is capable of storing at least the amount of one line of a digital image taking signal by means of a memory control circuit 107. It can also read out from a predetermined location (i.e., address). 105 is a digital signal processing portion with a built-in A/D converter, generating a final output image signal.
Note that the digital image taking signal stored in the memory remains to have a greater number of pixels than the standard image size. The memory control circuit 107 is able to obey control commands from the micon (i.e., microcomputer) 130 to select the lead pixels which is read out from the memory 106, and is configured so as to read out only an amount equal to the standard image size.
Reference numeral 130 is a camera control micon, and it performs control of the camera system as a whole. However, in order to simplify the diagrams, only the portion relevant to the blur correction has been shown here. Further, the detection of the vibration is made along two axes of pitch (i.e., a vertical axis) and yaw (i.e., horizontal axis). However, since exactly the same control is being performed in two axes, only one direction has been shown here.
Reference numeral 121 is an angular velocity sensor, and it detects vibration of the camera. 123 is an amp, and it amplifies the detected angular velocity signal.
Reference numeral 125 is an A/D converter built into the micon 130, whereby a two-directional angular velocity signal is converted into a digital signal and becomes angular velocity data. 126 is an HPF (i.e., high pass filter) for performing a DC cut, and 127 is a filter for performing phase compensation. 129 is an HPF for panning control and other such controls, in which the cut off frequency is variable. When panning is performed, the value of output from an integrator is stuck in one direction, and it does not quite return to normal state upon finishing panning, whereby the hand vibration correction ceases to be effective. Therefore, a correction control unit 131 judges the status of the panning based on the size of the output from the integrator 128, and while panning the cut off frequency of the HPF 129 is shifted to a higher frequency region in response to the size of the output from the integrator 128, and whereby producing a result that low-frequency elements produced while panning are cut and a control is applied so that the integral output does not get stuck. As a result, it becomes possible to perform good blur correction during the pan process and after panning, as well.
Predetermined signal processing is performed on the angular velocity data by means of the HPF 126, the phase compensator 127 and also the HPF 129 having the variable cut off frequency, and the integrator 128 generates a vertical and horizontal vibration correction signal.
A correction system control unit 141 transmits the vertical vibration correction signal to the CCD driving circuit 104 and the horizontal vibration correction signal to the memory control circuit 107, each from the output from the integrator 128. As described above, the CCD driving circuit 104 and the memory control circuit 107 each adjust the cut out position in response to the vibration correction signal.
As a result of this series of operations, a standard image size such as 502 or 504 is adjusted away from the center and cut out from the entire image size 501 as shown in FIG. 11, and as a result it becomes possible to correct an image blur resulting from hand vibration and the like.
However, in the case when an electronic blur correction apparatus is used, the blur correction can only be performed per field, so the vibration which occurs during the CCD storage remains in the picture as image deflection. If the shutter speed is made to be faster then this Is almost unnoticeable, and in conventional electronic blur correction apparatuses, a method is generally used in which the shutter speed during correction is constantly kept above a certain reference speed. However, due to the recent trend toward increasingly compact and light construction, the amplitude of the hand vibrations is greater, and the vibration frequency can easily become higher, so the image deflection of the picture can no longer be ignored. FIG. 13 is a diagram depicting residual vibration between fields in a case when there is hand vibration having a frequency of 7.5 Hz, which clearly shows that even if the shutter speed is made to be fast, the larger the hand vibrations are the greater the amount of the residual vibration is. In this way, when the amplitude of the vibrations is large the amount of image deflection in the picture becomes large, and even though the correction is working in the picture itself, a phenomenon is generated such that pictures with image deflection and pictures with no such image deflection are produced alternately, and the picture appears as if the focus were unstable or were constantly shifted, and further, since the focus appears as if it were unstable or were constantly shifted it also appears as though the blur correction unit were creating vibrations. Note, however, the frequency at this time is a maximum of 30 Hz (since the minimum cycle is one frame), regardless of the frequency of the hand vibrations of the operator. Therefore, the more precise the hand vibration correction is, the more conspicuous the phenomenon described above becomes, so there was a problem that the quality of the hand vibration correction function and the auto-focus function appeared to have declined.